An igniter for a gas turbine engine should be capable of reliably and cost-effectively igniting a combustible mixture during numerous starts that occur throughout operational cycles of the engine. The igniting function is generally accomplished by electrically-generating a spark across a gap formed between oppositely charged electrodes in a retractable igniter rod. The igniter rod may be a slender columnar structure, which in an ignition-position is deployed into a path of the combustible mixture (e.g., hot gas path) in a combustion chamber. The ignition takes place when velocity and pressure of compressed air in the chamber reach predetermined values.
After ignition, the igniter rod is designed to retract (e.g., to a retracted-position) into a protective structure (e.g., a guide tube) away from the hot combustion environment in response to continued compressor discharge pressure in the chamber throughout a working operational cycle of the engine.
The igniter may be internally equipped with a compression spring and a movable piston, as may be assembled in the guide tube of the igniter so that the igniter rod remains subject to compression force from the spring in the retracted position during working operation of the engine. Force from the compressed spring would return the igniter to the ignition-position after engine shutdown, such as when compressor discharge pressure is discontinued and the air pressure in the chamber essentially returns to ambient conditions.
The generally slender columnar structure of the igniter rod could make it susceptible to vibration, which commonly develops during normal engine operation, and/or to a load magnification due to cantilever beam loading. In certain situations, side loading (e.g., due to gravity on the igniter rod and/or the weight of electrical cables suspended at the cold-end of the rod), could lead to undesirable mechanical-pinching conditions between the moving piston and the guide tube or could affect the integrity of a threaded-connection (located proximate the hot environment) between the piston and the igniter rod.
It is standard practice that for reliable and cost-effective operation, the igniter may include components which may need periodic replacement during the life of the igniter. For example, the igniter rod may be replaced often during the life of the igniter due to sparking life limitations of the electrodes.
In view of the foregoing considerations, it would be desirable to provide improved mechanical structures for gas turbine igniters, as, for example, may eliminate or substantially reduce the foregoing effects. It would be further desirable to provide relatively low-cost and user-friendly mechanical structures as may be conducive to reliable and quick-replacement of components, which may need replacement during the life of the igniter.